In recent years, as early detection and diagnostic accuracy for lesions using endoscope examination has been improved and various treatment tools included in an endoscope have been developed, further performance improvement of the endoscope is highly expected. However, image data of the inside of a coelom imaged by the endoscope is communicated to a display device, which is provided in a position away from the endoscope, via an image transmission cable (hereinafter referred to as cable). Thereby, a positional relationship among a surgeon, a subject, and the display device is limited due to the cable.
An endoscope that overcomes the limitation of a positional relationship among a surgeon, a subject and a display device by wirelessly transmitting data of an image acquired by image pickup using the endoscope to the display device has been proposed (e.g., see Patent Document 1).
Here, when moving image data of the inside of a coelom acquired by image pickup using the endoscope is compressed and the compressed moving image data is transmitted from the endoscope to the display device, the moving image data is usually encoded by rearranging an image frame order (hereinafter referred to as reordering) in a moving image data compression process, such as MPEG (Moving Picture Experts Group). This requires, for example, an input waiting time for image frame data in the compression process. Accordingly, a delay of a display time (hereinafter referred to as display delay) occurs between an actual motion in the coelom and a displayed moving image.
However, if a still image of the inside of the coelom is acquired by image pickup, it is difficult for a surgeon, who is manipulating the endoscope while watching the moving image transmitted from the endoscope, to accurately recognize image pickup timing for the still image as a display delay between an actual motion of an object to be imaged and a displayed moving image increases. Because of this, for the moving image data transmitted from the endoscope to the display device, it is desirable for reduction of the display delay to be prior to reduction of a data size. In a normal endoscope, a display delay of moving image data transmitted from the endoscope to a display device is reduced by using only an intra-frame compression process, such as I picture of MPEG or Motion-JPEG 2000, to eliminate reordering causing the display delay.
Meanwhile, with the improved early detection and diagnostic accuracy for lesions, high image quality is necessary for the still image data acquired by image pickup using the endoscope. Thereby, the still image data acquired by image pickup using the endoscope needs to be uncompressed data, lossless compression data without data loss caused by a decompression process, or lossy low compressed data with less data loss caused by the decompression process.
For the moving image data, since image frames are continuously updated, degradation of image quality is not particularly conspicuous, while for the still image data in which image frames are not updated, the degradation of the image quality is conspicuous, as seen from a comparison between the same image frames. Accordingly, the still image data needs to have higher image quality than the moving image data.